The invention relates to magnetic recording media and, in particular, control of surface characteristics of magnetic tape.
Magnetic tape is often used for storage and retrieval of data, and comes in many widths, lengths and formats. Magnetic tape remains an economical medium for storing large amounts of data. For example, magnetic tape cartridges or spools of magnetic tape are often used to back up large amounts of data for computing centers and the like. Magnetic tape cartridges also find application in the backup of data stored on smaller computers such as workstations, desktop computers and laptop computers.
The creation of magnetic tape typically involves a number of different processing steps. For example, a wide polymeric film typically undergoes a coating process in which one side of the polymeric film is coated with a nonmagnetic underlayer followed by one or more magnetic layers. The opposite side of the polymeric film is typically coated with a nonmagnetic backing layer. One or more of the layers coated on the film may include head cleaning agents (HCA) to increase the abrasivity of the tape, thus allowing the tape to remove debris from the read/write head of a tape drive during use. After coating, a calendaring process typically compresses and smoothes the coated materials on the tape. The tape is then typically cut in a slitting process to realize a number of narrow magnetically coated tape strands cut to the desired width. In this disclosure, a xe2x80x9ctape pancakexe2x80x9d refers to a spool of magnetic tape that has been cut to a desired width.
Each individual tape pancake can be burnished, for example, by scraping, vaming, lapping, or a combination of different burnishing techniques. Burnishing further smoothes the tape surface and has been shown to significantly improve performance of magnetic tape by reducing the number of reading and recording errors. Scraping techniques typically involve feeding the tape past a scraping mechanism (scraper) to smooth or alter the surface of the tape. Vaming techniques utilize a rotating cylinder that rotates in a direction opposite the direction of incoming tape. The rotating cylinder, for example, is typically coated with industrial grade diamonds or another abrasive material to smooth or alter the surface of the tape as it passes by and contacts the rotating cylinder. Lapping techniques utilize a lapping film that is fed in a direction opposite the direction of incoming tape. For example, the lapping film may pass in one direction over a supporting structure referred to as a lapping shoe. The tape is passed over the lapping shoe in the opposite direction. The lapping shoe forces the lapping film into contact with the surface of the tape as the tape and lapping film feed past one another in opposite directions. In this manner, the lapping film can be used to effectively burnish the surface of the tape.
After burnishing the tape is typically wiped clean and then degaussed in a degaussing process. If desired, servo patterns can be magnetically written on the tape, and the tape may be spooled into a cartridge, which can then be sold as a magnetic tape cartridge. Alternatively, the burnished tape pancake may be sold with or without servo patterns written on the tape.
Abrasivity is a measure of the abrasive characteristics of magnetic tape, and is an important quality required to meet magnetic tape specifications associated with a given recording system. If abrasivity is too low, the magnetic tape may not adequately remove dust and debris from a read/write head, which can cause clogging in the read/write head during use. However, if abrasivity is too high, the tape may actually harm the read/write head during use, for example, by changing the shape of the head.
Abrasivity of magnetic tape is typically quantified by the amount of wear that the tape causes on an object formed from a specified material. For example, tape can be fed over the object at a particular speed and tension, for a defined amount of time. The amount of wear on the object as a result of contact with the tape can be used to quantify the abrasivity of the tape. The amount of wear is typically specified to ensure that the tape will function properly in a given system.
Abrasivity of magnetic tape is a complex characteristic which depends on tape particles and binder formation, tape surface, tape tension and tape speed during the coating process, head materials, humidity and temperature. The amount of head cleaning agent (HCA) in the coating formula is conventionally the main factor used to control abrasivity of magnetic tape. For example, if abrasivity of the magnetic tape is not within specification, the formula for one or more of the coatings can be modified by increasing or decreasing the amount of HCA. Adjusting the amount of HCA, however, may also affect other properties of the magnetic tape. In particular, since the thickness of magnetic layers on the tape are thin, being in the neighborhood of 10 microinches, HCA with an average sizes of about 12 microinches may stick out even after calendaring, which may affect properties of the tape such as roughness, friction, or other properties of the magnetic tape.
In general, the invention is directed to techniques for controlling the abrasivity of magnetic tape without modifying the coating formulas used to create the magnetic tape. For example, the invention may involve controlling or adjusting the abrasivity of magnetic tape using one or more burnishing techniques such as lapping, vaming or scraping. In this manner, the abrasivity of magnetic tape can be controlled or adjusted to ensure that the tape meets the necessary tape specifications without modifying the coating formulas applied during the coating process. Coating is a relatively complicated process where all the coating parameters are interrelated. However, tapes coated to exhibit many optimal features often have abrasivity higher than desired values. The invention provides a simple and effective way to improve tape abrasivity without degrading other tape qualities.
Abrasivity refers to a measure of the abrasive characteristics of magnetic tape and is typically quantified by tape manufactures or makers of magnetic recording systems to ensure that the magnetic tape has acceptable abrasive characteristics. An acceptable level of abrasivity can improve the performance of a magnetic tape system by enabling the magnetic tape to remove dust or debris from the magnetic head as the magnetic head reads or writes onto the magnetic tape. Acceptable levels of abrasivity, however, are limited. If abrasivity is too high, then the magnetic tape can wear down the magnetic head, and in some cases actually change the shape of the head, which is undesirable.
In one embodiment, a method includes selecting a burnishing variable according to an acceptable level of abrasivity for magnetic media. For example, selecting the burnishing variable may comprise selecting a lapping film to be used for lapping of the magnetic media, selecting a material for a rotating cylinder to be used in vaming of the magnetic media, or selecting a scraper to be used in scraping the magnetic media. The method may also include burnishing the magnetic media according to the selection. For example, upon selecting an acceptable lapping film, burnishing the magnetic media comprises lapping the magnetic media using the selected lapping film.
A number of different burnishing variables can be selected, including any variable that affects the level of burnishing. For example, in the case where burnishing is performed using lapping techniques, additional burnishing variables that can be selected may include one or more additional lapping films, a configuration for a lapping shoe, a level of tension for the magnetic tape as it passes over the lapping shoe, a speed for the lapping film, a speed for the magnetic tape, and a level of engagement for the lapping shoe. Sizes, shapes of the grits and the type of lapping films can also affect abrasivity of the tape. In some cases, the invention may involve selecting a number of these variables and then burnishing the magnetic media according to the selections. Similar variables can also be selected if other burnishing techniques, such as vaming or scraping are used. Favorable burnishing variables can be determined experimentally to ensure that the magnetic tape meets specification.
The method may also include coating a formula which includes head cleaning agents, such as alumina (Al2O3), on a polymeric film to create the magnetic media.
The invention can provide a number of advantages. For example, the invention can provide a simple and cost effective way to adjust and control abrasivity in magnetic tape after the optimized coating conditions for the tapes have been obtained. Rather than create different coating formulas to achieve different abrasivities, the invention can use the same formula and adjust the abrasivity of the tape using burnishing techniques. In this manner, the tape manufacturing process can be simplified.
In addition, the invention can be used to more easily create magnetic tape having acceptable abrasivity, while at the same time meeting other tape specifications. As mentioned, conventional techniques control and adjust abrasivity by modifying the coating formulas. For example, abrasivity is conventionally increased by adding more head cleaning agents (HCA) to a coating formula used to coat a magnetic layer on the tape.
The additional HCA, however, often affects other magnetic tape properties because additional HCA changes the number of magnetic particles in the formula per unit volume. Since the invention does not require modification of the formula to adjust abrasivity, the other magnetic tape properties may remain unaffected. Thus, if a particular magnetic tape meets most tape specifications, but has an abrasivity that is too high, the invention provides a simple solution. In that case, the tape could simply be burnished by an amount sufficient to reduce the abrasivity accordingly, leaving other tape properties intact. Choice of the burnishing variables, however, may need balance both desired abrasivity and error reduction (or dropout, which is the conventional reason for burnishing). In other words, too much burnishing may reduce abrasivity significantly at the expense of the reduction of errors.
Additionally, the invention can use the same coating formula in creating magnetic tapes having different abrasivities. Thus, tapes for two different magnetic recording systems can be created to have different levels of abrasivity using the same coating formula. In this manner, the creation of a number of different coating formulas can be avoided. Moreover, changes in abrasivity can be accomplished on a post-coating basis as needed. Another advantage of the invention is that it can smooth and clean the surface of the tape, and at the same time, achieve desired levels of abrasivity.
Additional details of various embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.